Recently, more and more the phenomenon can be observed that the order-picking systems requirements, particularly in the field of retail, are getting higher and higher with respect to the performance of the system. The number of picking orders to be processed each day rises steadily. The number of pieces per order line decreases, but the total numbers of pieces are increasing each day. This means that modern order-picking systems have to handle bigger and bigger picking-order performances, wherein the requirements with respect to the dynamics are getting higher and higher. Previously, if branches have waited up to one week until they have transmitted their orders (in a corresponding size) to a central warehouse, nowadays (a lot of smaller) orders are occasionally issued in an hourly rhythm. This means that at the end of the order-picking systems one has to react flexibly. Request peaks have to be balanceable by a corresponding performance.
Typically, corresponding order-picking systems are operated in accordance with the principle of “goods-to-man”, in order to allow provision of the required output. Now, if a number of smaller orders is to be processed with a spectrum of articles which gets broader and broader, bigger warehouses and more and more storage movements are required for allowing collection of article units or packing units (in accordance with a picking order) and shipping preparation. For example, a bottle of water is a typical article unit. For example, a box of water is a typical packing unit. A number of water boxes can form a storage unit. A storage unit is a handling unit as employed in the warehouse. A storage unit is typically provided by one sort only (for example only water boxes), but can comprise articles of different types as well. The storage unit typically comprises a load support (pallet, tray, container, etc.) and the load (for example, one layer of water boxes).
A storage movement is a process during which a storage unit is moved between two storage elements, for example, between a rack and a storage machine.
All these requirements increase the handling effort while picking orders are processed in order-picking systems of the type discussed here. Therefore, one tries to obtain a maximum of automation.
The sequence according to which the article units or packing units are provided at the packing station is to be considered as another criterion. The customer either wants the articles to be packed in a pre-given sequence on a shipping pallet or into a shipping container, in order to allow removal (at the customer's site) in accordance with a desired sequence, or the customer wants light and fragile articles to be packed last or on top. Huge numbers of pieces require provision of the articles at a sufficient velocity and in the right sequence (i.e. sequencing is required) at the packing station.
The German patent application DE 197 12 839 A1 exactly deals with this kind of problems, and proposes, for the purpose of solving them, an automated order-picking system comprising a container warehouse having racks, a conveyor (elevator at front ends of the racks) for transportation of containers from the container warehouse to a plurality of order-picking stations, and a distribution system provided therebetween.
Although the system proposed in the document DE 197 12 839 already achieves relatively high performances (transportation of containers per hour), performance requirements, as to be fulfilled nowadays, cannot be achieved therewith. This is reasoned in that the distribution system has to supply articles or containers to many workstations. On the other hand, additional vertical buffers have to be installed in respective conveyor branches between the distribution system and the workstations, in order to allow the sequencing. The distribution system—and therefore also the warehouse being arranged in front of it—sometimes conveys articles, or better to say containers, in a non-sequenced manner towards the workstations, because the warehouse—under the required performance—would not be capable of outputting sufficient containers in the right sequence within the pre-given time. Further, it is required that containers, which have been transported to the workstation for the purpose of removing articles, are transported back in the rack again after the removal of articles. This happens also via the loop-like distribution system so that the transportation performance of the distribution system is correspondingly decreased, since the transportation of the articles in both directions occurs via the same track.
Another conventional order-picking system, working in accordance with the principle of “goods-to-man”, is disclosed in the German patent application DE 10 2004 014 378 A1.
There, so-called storage containers are transported from a container warehouse to an order-picking station. An operator removes articles from the container, and puts them in so-called picking buckets. The picking buckets are arranged above a conveyor belt. As soon as all of the articles required for processing a picking order have been collected in one of the picking buckets (manually), the picking bucket opens downwards, and releases the articles on the conveyor belt. The conveyor belt itself is endlessly rotating, and provided with a plurality of separation strips on its surface. The separation strips separate the conveyor belt into a plurality of sections allowing collection of articles, all belonging to one picking order. The separation strips prevent a mixing of articles belonging to different picking orders. The conveyor belt delivers the so-collected articles at an end thereof to so-called order containers. Also this system is not capable of providing the order-picking performance required today. Additionally, in this system the size of articles, which can be handled, is heavily limited by the bucket size.
The German patent application DE 10 2004 058 216 A1 relates to a picking-order arrangement, particularly dedicated to drugstores, having at least one rack comprising a plurality of rack compartments each of which is formed to receive an article, particularly a drug, and at least one movable transportation device connected to a positioning device and adapted to receive an article and to move same into a rack compartment.